New worlds in our solar system
Asteroids and comets form the largest and,
perhaps paradoxically, the least well known population of celestial bodies in
our solar system. The shortage of detailed information is mainly due to the
fact that, because of the large interplanetary distances,
disk-resolved images can be obtained
only of a limited number of these targets.
Nevertheless, our view of this population has started to
change dramatically. Spacecraft
images and radar observations, though few and far between,
have already revealed to us that asteroids come in just about all possible
shapes, configurations, and structures.

The need for a large number of detailed asteroid models is now pressing,
so all possible data sources are valuable. A hitherto much unused
but major and easily available source of information on small solar
system bodies consists of their photometric lightcurves, i.e., measurements of
their total brightnesses that vary
as the viewing/illumination geometry changes. The inverse problem
of determining the object's shape, its rotational state, and the
scattering properties of its surface
from lightcurves is notoriously demanding.

We have shown that advanced methods can produce
detailed asteroid models that are even
comparable to those obtained with radar imaging.
Our results also match the `ground truth'
from the few space probe fly-by missions very well, so the inversion
method has been well tested. Indeed, we can now well say that
the resolving capacity of lightcurve inversion lies between
space telescope and radar, and its
range extends from near-Earth to main-belt asteroids. Our approach has
also opened up a whole new possibility of including
complementary data in multidatainversion
from various sources that would otherwise
be insufficient alone: combined with photometry,
these will allow the building of increasingly detailed models.

Besides their obvious part in completing the picture of our solar system at
present, asteroids and comets are also important sources of
cosmogonical information. Their rotation states and physical structure offer
direct views of the evolution and primordial stages of the solar system.